Add old_name field to AuditEntry

[lmartinking]

This field is used when a repository is renamed.

Fixes: #2844.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[gmlewis]

Please run go generate ./... in the top of this repo and push (not force-push) the changes to this PR.
See CONTRIBUTING.md for details.

[lmartinking]

@gmlewis I've run the codegen, as well as rebased against main

[codecov]

Codecov Report

Merging #2843 (b185d31) into master (7e3bb17) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2843   +/-   ##
=======================================
  Coverage   98.06%   98.06%           
=======================================
  Files         138      138           
  Lines       12318    12318           
=======================================
  Hits        12080    12080           
  Misses        162      162           
  Partials       76       76           

Files Changed	Coverage Δ
github/orgs_audit_log.go	100.00% <ø> (ø)

[gmlewis]

Thank you, @lmartinking !
LGTM.
Merging.